Severe and potentially dangerous shortages in the blood supply are common. This problem is expected to worsen as the population ages (increasing demand) and more and more stringent restrictions are placed on blood donor eligibility (decreasing supply). A crucial component of the effort to meet the increasing demand for blood is the ongoing recruitment of new donors. Ideally, new recruits would become lifelong donors, contributing up to six times per year and hundreds of units of blood in a lifetime. Unfortunately, less than half of all novice donors will ever provide a second donation. Because the experience of vasovagal reactions (e.g., dizziness, weakness, lightheadedness) is one of the strongest predictors of attrition in novice donors, prevention of such reactions may be a particularly efficient and enduring method of enhancing the nation's blood supply. Our long-term objective is to provide blood collection agencies with simple and inexpensive strategies that can be used to prevent vasovagal reactions and enhance donor retention. The specific aim of the current proposal is to evaluate the combined effects of two particularly promising vasovagal prevention strategies - water loading and applied muscle tension. We will compare vasovagal reactions to blood donation and repeat donation behavior in 400 first-time donors assigned to either active treatment (pre- donation water loading and muscle tensing during donation) or placebo treatment (pre-donation muscle tensing). Participants will be recruited and tested at American Red Cross fixed and mobile blood donation clinics held in rural and urban settings. Vasovagal reactions will be measured using on-site donor and phlebotomist ratings as well as donor ratings obtained 24 hours later. Using the American Red Cross national donor database, subsequent donation history will be tracked during a two-year follow-up period. We hypothesize that participants in the active treatment group will experience less adverse reactions and will be more likely to return to provide a new donation as compared to participants in the placebo group. The proposed study tests simple strategies that volunteer blood donors can use to prevent negative reactions, such as fainting, that frequently discourage donors from returning. The long term goal of our work is to address recurrent shortages in the blood supply by increasing donor motivation and commitment to lifelong giving. Because we are working directly with the American Red Cross, our findings can be quickly translated into practice.